1. Technical Field of the Invention
The invention relates to a suspension stop for a vehicle suspension arm, in particular for a telescopic suspension arm of a motor vehicle steered wheel, provided with a bearing and means of protecting this bearing.
2. Prior Art
Traditionally, suspension stop bearings are housed in casings in two parts, closed by sealing lips fixed to one of the parts of the casing and sliding over the other part of the casing, as illustrated in the document EP 1 000 781. This technology has the disadvantage of causing a sliding torque between the rotating parts, referred to as drag torque, which is particularly detrimental in applications to steered wheels.
To eliminate this drag torque, it has been proposed to replace the traditional sealing linings with contactless chicane devices, that is to say devices in which the rotating elements are interleaved in one another, without contact, so as to create a significant pressure drop between the outside and the bearing housing. A first example of this type of technology is offered by the document FR 2 857 906, which describes a suspension stop for a suspension arm with a coil spring, comprising a stop bearing defining a rotation axis of the device and provided with a bottom metal washer turning with respect to a top metal washer. A support piece made from synthetic material is disposed between the coil spring and the bearing to transmit the forces exerted by the spring to the bottom washer. A cover covers the top washer and delimits with the support piece a housing for the bearing. The cover is provided with a cylindrical skirt covering, without contact, a cylindrical peripheral zone of the support piece and delimiting a pressure drop device between the housing and the outside. The simple structure of the pressure drop device makes it possible to accommodate relative movements between the cover and the support piece, movements that are due in particular to the low rigidity of the bearing washers. However, ingress of liquid by capillarity is not excluded and the seal is not of good quality.
To make it possible, without friction and without significantly increasing the axial and radial bulk, to ensure a good-quality seal between the rotating elements of a suspension stop, there was proposed in the document FR 2901179 a suspension stop device for a suspension arm of a vehicle, the arm being provided with a coil spring, the device comprising: a rigid stop bearing defining a rotation axis of the device and provided with a bottom metal washer turning with respect to a top metal washer; a support piece made from synthetic material for transmitting to the bottom washer the forces exerted by the spring, the intermediate support piece comprising an annular support area for the bottom washer; and a cover covering the top washer and delimiting with the support piece a housing for the bearing, the cover being provided with a skirt covering without contact a peripheral area of the support piece and delimiting with the peripheral area of the support piece an annular labyrinth, disposed radially outside the housing and connecting the housing to the outside, the annular labyrinth comprising successively, from the inside to the outside of the housing, a first annular pressure drop device with radial clearance J1, a second annular pressure drop device with radial clearance J2, and a third annular pressure drop device with radial clearance J3. The rigidity of the bearing makes it possible to achieve relatively small clearances, without risk of friction at the labyrinth.
Another solution explored in the document WO 2009/019340 for both avoiding risks of uncontrolled friction at the labyrinth in the case of deformation of the parts and the excessive friction of a peripheral sealing lip, consists of disposing a sealing element in the space between the cover and the spring support, sized so as to be in rubbing contact firstly with the cover and secondly with the spring support, said sealing element being mounted so as to be able to move with respect at least to the spring support or to the cover.
However, new practices with regard to washing of vehicles and in particular washing the underside of the body by high-pressure water jet, shift the requirements with regard to protection of suspension stop bearings.